Alginate-immobilised algal wastewater treatment enhanced by species selection

Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment

Efficient wastewater treatment accompanied by sustainable "nutrients/pollutants waste-wastewater-resources/energy nexus" management is acting as a prominent and urgent global issue since severe pollution has occurred increasingly. Diverting wastes from wastewater into the value-added microalgal-biomass stream is a promising goal using biological wastewater treatment technologies. This review proposed an idea of upgrading the current microalgal wastewater treatment by using immobilized microalgal system. Firstly, a systematic analysis of microalgal immobilization technology is displayed through an in-depth discussion on why using immobilized microalgae for wastewater treatment. Subsequently, the main technical approaches employed for microalgal immobilization and pollutant removal mechanisms by immobilized microalgae are summarized. Furthermore, from high-tech technologies to promote large-scale production and application potentials in diverse wastewater and bioreactors to downstream applications lead upgradation closer, the feasibility of upgrading existing microalgal wastewater treatment into immobilized microalgal systems is thoroughly discussed. Eventually, several research directions are proposed toward the future immobilized microalgal system for microalgal wastewater treatment upgrading. Together, it appears that using immobilization for further upgrading the microalgae-based wastewater treatment can be recognized as an achievable alternative to make microalgal wastewater treatment more realistic. The information and perspectives provided in this review also offer a feasible reference for upgrading conventional microalgae-based wastewater treatment.

Nitrogen removal from wastewater by an immobilized consortium of microalgae-bacteria in hybrid hydrogels

The high content of nitrogen in wastewater brings some operational, technical, and economical issues in conventional technologies. The aim of this study was to evaluate the nitrogen removal by hybrid hydrogels containing consortium microalgae-nitrifying bacteria in the presence of activated carbon (AC) used as an adsorbent of inhibitory substances. Hybrid hydrogels were synthesized from polyvinyl alcohol (PVA), sodium alginate (SA), biomass (microalgae-nitrifying bacteria), and AC. The hybrid hydrogels were evaluated based on the change in ammonium (NH₄), nitrate (NO₃), and chemical demand of oxygen (COD) concentrations, nitrification rate, and other parameters during 72 h. Results indicated that NH₄ removal was more effective for hydrogels without AC than with AC, without significant differences regarding consortium biomass concentration (5 or 16%), presenting final concentrations of 3.13 and 3.75 mg NH₄/L for hydrogels with 5 and 16% of the biomass, respectively. Regarding NO₃ production, hydrogels without AC reached concentrations of 25.9 and 39.77 mg NO₃/L for 5 and 16% of the biomass, respectively, while treatments with AC ended with 2.17 and 1.37 mg NO₃/L. This confirms that hydrogels can carry out the nitrification process and do not need AC to remove potential inhibitors. The best performance was observed for the hydrogel with 5% of biomass without AC with a nitrification rate of 0.43 mg N/g TSS·h.

A review on the sustainable procurement of microalgal biomass from wastewaters for the production of biofuels

The feasibility of microalgal biomass as one of the most promising and renewable sources for the production of biofuels is being studied extensively. Microalgal biomass can be cultivated under photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic cultivation conditions. Photoautotrophic cultivation is the most common way of microalgal biomass production. Under mixotrophic cultivation, microalgae can utilize both organic carbon and CO2 simultaneously. Mixotrophic cultivation depicts higher biomass productivity as compared to photoautotrophic cultivation. It is evident from the literature that mixotrophic cultivation yields higher quantities of polyunsaturated fatty acids as compared to that photoautotrophic cultivation. In this context, for economical biomass production, the organic carbon of industrial wastewaters can be valorized for the mixotrophic cultivation of microalgae. Following the way, contaminants' load of wastewaters can be reduced while concomitantly producing highly productive microalgal biomass. This review focuses on different aspects covering the sustainable cultivation of different microalgal species in different types of wastewaters.

Data-driven analysis on immobilized microalgae system: New upgrading trends for microalgal wastewater treatment

Microalgal immobilization is receiving increasing attention as one of the most viable alternatives for upgrading conventional wastewater treatment. However, an in-depth discussion of the state-of-the-art and limitations of available technologies is currently lacking. More importantly, the reason for the hesitant development of immobilized microalgae for wastewater treatment remains unclear, which hinders its practical application. Thus, comprehensively understanding and evaluating details on immobilized microalgae is urgently needed, especially for the current advances of immobilization of microalgae in wastewater treatment over the last few decades. In this review, scientometric approach is used to explore research hotspots and visualize emerging trends. Data-driven analysis is used to scientifically and methodically determine hotspots in the current research on immobilized microalgal wastewater treatment, along with that the implicit inner connection underlying the frequent co-occurring terms was explored in depth. Four hotspots focusing on immobilized microalgae for wastewater treatment were identified, mainly demonstrating: (1) main factors including light, temperature and immobilization methods would majorly affect the treatment performance of immobilized microalgae; (2) immobilized microalgae membrane bioreactor, immobilized microalgae-based microbial fuel cell and immobilized microalgae-based bed reactor are three dominant treatment systems; (3) immobilized microalgae have a higher robustness and tolerance for treating various types of wastewater; and (4) a complete sustainable circle from wastewater treatment to resource conversion via the immobilized microalgae can be achieved. Finally, several new directions and new perspectives that expose the necessity for fulfilling further research and fundamental gaps are pointed out. Taken together, this review provides helpful information to facilitate the development of innovative and feasible immobilized microalgal technologies thus increasing their viability and sustainability.

Recent advances in polymer composite, extraction, and their application for wastewater treatment: A review

Wastewater from diverse industrial sectors, agricultural practices and other household activities causes water pollution that result in different environmental issues. The main goals of wastewater treatment are typically to enhance the purity of wastewater and to enable the disposal of domestic and industrial effluents without endangering human health or causing excessive environmental issues. There were several natural and synthetic materials which have been utilized for wastewater treatment, amongst them polymers gain more importance due to their non-toxicity, economic feasibility, abundant availability of sources, renewability, biocompatibility, biodegradability, etc. The organic polymers such as cellulose, chitin, gelatin, alginates, lignin, dextran and other starch derivatives are the most commonly used natural polymers in wastewater treatments. The unique physical and chemical characteristics of the natural polymers make them become an alternative in wastewater treatments such as membrane filtration, adsorption, coagulation, flocculation and ion-exchange process to remove harmful contaminants such as toxic metals, dyes, medicines, pesticides, and so on. The review article discusses natural polymers and related uses in wastewater treatment. This review mainly focused on the wastewater treatment using natural polymers and the techniques involved for their extraction from natural sources. The recent trends in polymer extraction from the natural sources and the scope for the future research of natural polymers in various sectors are also discussed in detail.

Recent advances in starch-based magnetic adsorbents for the removal of contaminants from wastewater: A review

Considerable concern exists regarding water contamination by various pollutants, such as conventional pollutants (e.g., heavy metals and organics) and emerging micropollutants (e.g., consumer care products and interfering endocrine-related compounds). Currently, academics are continuously exploring sustainability-related materials and technologies to remove contaminants from wastewater. Magnetic starch-based adsorbents (MSAs) can combine the advantages of starch and magnetic nanoparticles, which exhibit unique critical features such as availability, cost-effectiveness, size, shape, crystallinity, magnetic properties, stability, adsorption properties, and excellent surface properties. However, limited reviews on MSAs' preparations, characterizations, applications, and adsorption mechanisms could be available nowadays. Hence, this review not only focuses on their activation and preparation methods, including physical (e.g., mechanical activation treatment, microwave radiation treatment, sonication, and extrusion), chemical (e.g., grafting, cross-linking, oxidation and esterification), and enzymatic modifications to enhance their adsorption properties, but also offers an all-round state-of-the-art analysis of the full range of its characterization methods, the adsorption of various contaminants, and the underlying adsorption mechanisms. Eventually, this review focuses on the recycling and reclamation performance and highlights the main gaps in the areas where further studies are warranted. We hope that this review will spark an interdisciplinary discussion and bring about a revolution in the applications of MSAs.

Performance of an immobilized microalgae-based process for wastewater treatment and biomass production: Nutrients removal, lipid induction, microalgae harvesting and dewatering

Immobilized microalgae are good for wastewater treatment and biomass production. This study investigated treatment efficiency of a continuously operated system employing immobilized microalgae for secondary effluent of wastewater treatment plants, as well as the effectiveness on induction of valuable products, harvesting and dewatering of microalgae biomass. Under semi-continuous operation condition, microalgal dry weight increased 4.75 times within 2 d, associated with the highest removal rate of ammonia and phosphate at 28.95 mg/L·d and 4.83 mg/L·d, respectively. An immobilized microalgae membrane bioreactor (iMBR) was continuously operated for a month. The harvested immobilized microalgae beads were transferred to induction stage to obtain 4.5 times increase of lipid content per cell within 2 d. Immobilized microalgae performed 1.9 cm/s settling velocity and 97% water removal efficiency around 40 °C. A prospective integrated process on resource recovery and carbon neutrality was proposed for wastewater treatment, induction, harvesting and dewatering of immobilized microalgae cells.

Direct processing of alginate-immobilized microalgae into polyhydroxybutyrate using marine bacterium of Saccharophagus degradans

Alginate immobilized microalgae (AIM) was found efficient in algal cells separation and pollutants removal, however, its processing required alginate removal. In present study, polysaccharide-degrading bacterium of Saccharophagus degradans was used to biodegrade alginate and microalgae in AIM and produce polyhydroxybutyrate (PHB). Results showed that AIM cultivated in wastewater contained 34.0% carbohydrate and 45.7% protein. S. degradans effectively degraded and utilized polysaccharide of AIM to maintain five-day continuous growth at 7.1-8.8 log CFU/mL. Compared with glucose, S. degradans metabolism of mixed polysaccharide in AIM maintained the medium pH at 7.1-7.8. Increasing the inoculum concentration did not enhance AIM utilization by S. degradans due to the carbon catabolite repression of glucose which likely inactivated hydrolysis enzymes. PHB production in S. degradans peaked at 64.9 mg/L after 72 h cultivation but was later degraded to provide energy. Conclusively, S. degradans was effective in direct processing of AIM while showing potential in PHB production.